Search Documents

By Raymond A. Binns

Drilling into an active hydrothermal system linked to convergent-margin felsic magmatism is a listed priority of the Ocean Drilling Program that addresses several fundamental geoscience issues. Solid and fluid products of felsic rock-water interaction, and the consequences for global chemical fluxes and for ore deposition, should differ from those in basaltic mid-ocean ridge environments already successfully tested by Legs 106, 139, 158 and 169. So, too, will fracturing controls on fluid pathways, and sources for metals and ligands. Researching the subsurface volcanic, structural/hydrologic, and mineralisation/alteration architecture of a drilled felsic-hosted system also has economic implications, especially for land¬based mineral exploration. A first-order hypothesis to be tested states that fluids derived from volatile-rich magmas are more important than recirculated seawater in convergent-margin hydrothermal systems - economic geologists increasingly appeal to this for creating "world-class" massive sulfide orebodies. Another hypothesis proposes "subhalative" massive sulfide deposition within hydraulically expanded volcanic products as a factor in generating large orebodies. Many second-order hypotheses such as leaching fractionated volcanics to cause gold enrichment in back¬arc systems also need testing. The thoroughly surveyed, active, PACMANUS hydrothermal field in the Eastern Manus back-arc basin of Papua New Guinea will be the site for ODP Leg 193 commencing in November 2000. It lies near the crest (1655-1750 m) of high-standing Pual Ridge, a 40 km-long edifice of dacite/rhyodacite with basal andesite all having geochemical and isotopic affinities with modern arc volcanoes of nearby New Britain. PACMANUS includes at least three focussed, high-temperature "smoker" sites with Cu+Au-rich massive sulfide deposits, and a field of diffuse, lower temperature venting through intensely altered dacite where modelling indicates significant subsurface mineralisation. Isotopic characteristics of deposits and vent fluids suggest magmatic contributions to the mineralising fluids.

Jan 1, 2000

By Raymond Kaufman

While there is no immediate worldwide shortage of hard minerals, the consumption of natural resources is constantly increasing, and there are ominous predictions of shortages to come. Means of meeting rapidly increasing demands are being implemented. These include such methods as exploration and discovery of new ore bodies, development of new mines, increasing production at existing mines, working or reopening known deposits of lower grade ore and tailings, recycling old materials, and developing more efficient and less wasteful processes to convert ores and metals into useful products. The United States, although itself mineral-rich, depends in large measure on imports for many key minerals and basic materials derived therefrom. According to the Department of the Interior, the U. S. depends upon imports for more than half of its supply of six of the basic thirteen raw materials required by any industrialized society - aluminum, chromium, manganese, nickel, tin, and zinc. By 1985 the country will also depend upon imports for more than half of its iron and tungsten, and by the year 2000 imports will have to supply more than half of the copper, potassium, and sulfur that it requires.

Jan 1, 1975

By Burrows D. R.

Metal-rich sediments precipitating from hot saline brine pools were first discovered in 1965 in the Red Sea.1-2 The subsequent discovery of high temperature black smokers and associated massive sulphides in 1977 at latitude 21oN on the East Pacific Rise3 came more as a confirmation than a revelation. Formation of massive sulphides through precipitation from circulating sea-water had been predicted by Oftedahl in 19584, and the mechanisms well evaluated in basaltic-hosted Cyprus-type 5 and in Kuroko-type deposits.6,7 Sea-floor exploration from 1977 through the 1980?s in sediment-starved mid-oceanic ridge (MOR) settings had little impact on land-based exploration. This is primarily because: a) MOR spreading centres were recognized as poor analogies to even Cyprus-type basalt-hosted deposits; b) their preservation potential was limited due to rapid oxidation and c) the metallic deposits studied were small and therefore not directly comparable to the far larger ore bodies on land. More recently underwater mineral deposit research has focused in a variety of back-arc environments associated with felsic submarine volcanism, environments more similar to those predicted for the formation of Kuroko-type deposits (e.g. Okinawa Trough, 8 Lau Basin, 9 Manus Basin, 10 Aeolian arc, 11). Most studies, while scientifically interesting, were hampered, in general, by a lack of good descriptive data, a reliance on isolated grab samples, and a lack of sub-surface observations. This research has therefore had only limited direct impact on exploration strategies with the possible exception of research conducted in areas where faulting provided enhanced vertical exposures. 12

Jan 1, 2011

By Jung-Hoon Kang

Present study was stemmed from the survey associated with deep-sea mining in the KODOS area between Clarion Fracture Zone and Clipperton Fracture Zone located in the North Pacific Ocean. The study area, which is located in the southeastern part of North Pacific gyre, is oligotrophic waters with low nutrients and chl-a concentrations below 1µg/l (MOMAF, 1996). This area is also characterized by divergence at 8°N and convergence at 6°N, which moved northward or southward in the range of a few kilometers with seasonal and climate changes. If the waste materials related to deep-sea mining are intruded into the surface waters continuously, unexpected effects to water column ecosystem are anticipated negatively. In order to assess the impact on the planktonic ecosystem, natural variation need to be distinguished from anthropogenically induced variation in terms of the abundance and species composition of plankton. In this study, mesoscale variation of zooplankton community was reported in relation to the physical conditions in the northeastern Pacific during 1998 and 1999. Temperature and salinity were determined using a CTD from surface to 200m depth in July 3-20, 1998 and in June 22-July 1, 1999. Zooplankton samples were collected from two different depths (0-50m, 50-200m) by vertical towing using an opening-closing net (100cm diameter and 300 µm mesh size). The samplings were carried out at every one degree between 5° and 12°N (1998), between 5° and 11°N (1999) along the meridional lines of 131°30´ W. The net was lowered to the depth of interest from a stationary research vessel and towed upward to collect zooplankton at a speed of 25~30 m per minute. Zooplankton samples were transferred to 1-l sampling bottles and immediately fixed with neutralized formalin into the final concentration of 5%. Considering the characteristics of zooplankton such as diurnal vertical migration, all samplings were done during the nighttime. The volume filtered by the net was calculated from the readings of flow meter (Hydro-Bios Model 438-115). Zooplankton were identified to the genus level and enumerated under a microscope. The abundance of zooplankton at each station was expressed as the numbers/100 m3.

Jan 1, 2003

By Thomas Kuhn

The detailed investigation of both active and inactive submarine hydrothermal systems has gained tremendous progress during the last decades because of the increasing usage of remotely operated vehicles (ROV) as well as manned submersibles. Special aspects like the targeted sampling of chimney structures and vent fluids as well as the analysis of zonations of near-surface structures like sulfides mounds was only possible with the usage of such vehicles. However, the availability of such vehicles has been very limited because of the few number of deep-water ROVs and manned submersibles which need both a trained crew and a special research vessel. This was especially true for the German science community which did not have such devices at its disposal until recently. With the ROV QUEST 5 which is based at the University of Bremen (c/o. Prof. Dr. G. Wefer, Dr. V. Ratmeyer) this major drawback has now been eliminated.

Jan 1, 2003

By Sven Petersen, Berit Lehrmann, Bramley J. Murton, Paul A. J. Lusty

"INTRODUCTIONToday’s metal mining focusses on land based ore deposits which only consider one third of the Earth’s surface. Through an increasing global demand of strategic metals used in the electronic and green industry (Zepf et al. 2014), ‘uneconomic’ sites of lower grade in more technical challenging grounds such as greater depth and/or more remote areas are developed by the mining industry often resulting in higher environmental impact. However, considering the steady growth of the Earth population a shortage of certain metals may occur (Krausmann et al. 2009). In 2010, the United Nations allowed commercial exploration for seafloor massive sulphides (SMS) in international waters with currently six contractor licenses being granted.Although the number of discovered vent sites has steadily increased since the first discovery of hydrothermal venting at the Galapagos Rift in 1977 (Corliss et al. 1979) with more than 600 sites being known today, their economic potential is poorly constrained. So far Nautilus Minerals Inc., a Canadian mining company, is the only company having conducted a NI 43-101 resource estimate for the Solwara site, located in the territorial waters of Papua New Guinea. Other studies using bulk geochemical data from 95 sites published in literature do exist (Hannington et al. 2011, Monecke et al. 2016) suggesting a global resource potential for today’s known SMS deposits of 600 million tons with a median grade of 3 wt.-% copper, 9 wt.-% zinc, 2 g/t gold and 100 g/t silver. However, the geochemical data being used originated mainly from easily recoverable, mainly non insitu surface grab-samples and are under current mineral resource classification schemes such as JORC code or NI 43-101 not even accepted for resource estimations. Furthermore surface samples such as high-temperature sulphide chimney and talus material are not representative for the entire deposits with information regards thickness and continuity of individual sulphide layers obtained through drilling being scarce. In addition, it remains unknown what geological processes occur once hydrothermal activity ceases and whether metal tenor becomes enriched, depleted or disappears."

Jan 1, 2017

By Robert G. Ditchburn

Msjflkcisokng During the past sixteen years, GNS Science has developed a number of radiometric methods for dating massive sulfide samples from submarine arc and back-arc volcanoes. This has improved our understanding of the formation of these hydrothermal systems, the frequency and duration of their activity, and assisted marine mineral exploration companies in assessing the economic potential of these deposits that can be rich in copper, zinc and gold (up to 90 ppm Au in some chimneys). The radiometric dating methods that we employ utilize radium isotopes that are extracted from the host rocks without their parent thorium isotopes, by ascending, hot, acidic hydrothermal fluids. When the hydrothermal fluid discharges into cold seawater, chemically similar barium and radium co-precipitate as barite, a common mineral contained within the black smoker chimneys that grow upwards from the seafloor. From the onset of mineralization, the isotopes 228Ra and 226Ra (with half-lives of 5.75 yrs and 1600 yrs, respectively) begin to decay, so that the 228Ra/226Ra and 226Ra/Ba values decrease with time. Thus, samples can be dated using these ratios once the initial values, i.e., the values at the onset of mineralization, have been established, ideally from active chimneys. 228Ra decays to 228Th (half-life 1.91 yrs) and from the 228Th/228Ra values, the growth-rate of individual chimneys can be estimated. The isotope 210Pb (half-life 22.3 yrs) is occasionally used for dating the mineralization, although several samples from a chimney are needed to determine an age from the 210Pb grown from 226Ra, using the isochron technique.

Sep 14, 2011

By Mark Vardy, Kasia-Leigh Chidlow, Tim Minshull, Jeorg Bialas, Sven Peterson, Bramley Murton, Alba Gil

Since the discovery of the first black smoker on the East Pacific Rise in 1977 (Francheteau, et al., 1979), the hydrothermal vents, now called seafloor massive sulphides (SMS) deposits, have generated great interest in the geological community, especially regarding their formation and composition. SMS deposits are areas of hard substratum, with high base metal and sulphides content, that form through hydrothermal circulation and are commonly found at hydrothermal vent sites. The high base metal (Fe, Cu, Zn, Pb), sulphur-rich mineral content has interested mining companies, due to their potentially high economic value. Currently, the known SMS deposits do not have the same dimensions as the massive sulphides (MS) found on land (covering just 10s to 100s m2) and pose significant mining challenges (being located in water depths between 800 m and 6000 m), meaning that they do not appear to be economically exploitable at present. However, these deep-sea mineral resources could be important targets in the near future, particularly with our ever-increasing demand for base metals. A key aim of the European Union-funded Blue Mining project is to develop techniques to robustly quantify SMS deposits dimensions (both surface expression and subsurface extent) and therefore assessing the suitability of SMS deposits for future economically viable and environmentally clean deep-sea mining operations.

Jan 1, 2017

By Sven Petersen, Iain J. Stobbs, Bramley J. Murton, Paul A. J. Lusty

"INTRODUCTIONIt is widely thought that seafloor massive sulphide (SMS) deposits, the modern analogue of volcanogenic massive sulphide (VMS) deposits, present a potential global resource for base (Cu, Zn) and precious metals (Au, Ag). In addition, SMS deposits can be enriched in ‘critical metals’ including Se, Te, Tl [1], which are essential for use in the construction of modern and green technologies. Globally over 340 high temperature hydrothermal sites have been identified at a range of ocean spreading centres [2], significant massive sulphide deposit formation has been recorded at 165 of these sites [3].To date only 13 deep sea sulphide deposits have undergone intrusive investigation (drilling or coring) and of these, only 6 sites have published tonnage estimates [2]. Almost all research and drilling of SMS deposits has been focused on active systems, the investigation of the morphology, subsurface structure and mineralogy of hydrothermally extinct seafloor massive sulphide (eSMS) deposits is almost non-existent.As such, little is known about the mechanisms that operate post-SMS formation and which have an impact on the preservation and hence resource value of SMS. Identifying these generic processes and mechanisms, and the extent to which they impact the resource grade, is critical in evaluating the global potential of SMS."

Jan 1, 2017

By V. K. Banakar

The occurrence of hydrogenous ferromanganese encrustations (Fe-Mn crusts) on the Cretaceous age Afanasiy-Nikitin Seamounts (ANS) in the eastern Equatorial Indian Ocean (EEIO) was first reported by Banakar et al. (1997, Marine Geology). The major element composition of the samples from the upper flank of the ANS (~1650 m water depth) indicated enrichment of Co up to 0.9 % (Parthiban and Banakar, 1999, Indian Mineralogist). Subsequently a project supported by the Department of Ocean Development to explore the ANS for Co-enriched Fe-Mn crusts was launched in 2002 by the National Institute of Oceanography. Sampling at regular depth intervals along two transects on the slopes of the northern elevated region of the ANS was carried out. The Fe-Mn oxide deposition is evident on almost all types of substrates viz., basalts, conglomerate limestone, fossil corals etc., and the thickness of the oxide layer varies from a patina to 7 cm. The Fe-Mn crust growth is evident only above a water depth of 3200 m, below which semi-lithified carbonate ooze is dominant. The ANS Fe-Mn crusts from all the water depths exhibit Mn/Fe < 1.5 suggesting pure hydrogenetic accumulation of metal-hydroxides. Bulk sample Ce-contents for a few selected depth-representative samples are remarkably high, up to 3700 ppm with an average of ~2500 ppm. The positive Ce-anomaly decreases from ~8 at 1600 m depth to ~1.6 at 3200 m depth, which is in contrast to the modern dissolved oxygen depth-profile in the region. This observation suggests that major time-period of the Fe-Mn crust accretion history is dominated by ambient waters with lower-oxygen at deeper depths than at the intermediate depths. This in turn probably suggests a major reorganization in the deep-intermediate hydrography of the region in the past.

Jan 1, 2005

By Gérald Riverin

Over the past century, exploration methods for volcanogenic massive sulphide deposits have evolved in response to a decreasing number of discoveries made by traditional surface prospecting and by ground and airborne geophysics. Statistical trends support the concept that fewer and fewer outcropping and sub-cropping VMS discoveries will be made in the future. In turn, this creates new opportunities to develop more sophisticated exploration models and techniques to explore at greater depth and to make blind discoveries. Current exploration models include various combinations of geological, geochemical and geophysical criteria which have been based on the results of land-based VMS research. The role of seafloor research in the development of these models has so far been only of a subordinate nature, perhaps due to a lack of direct involvment of the exploration industry in the seafloor research, and vice-versa for the seafloor researchers in VMS exploration. Another contributing factor is that exploration relies on exploration criteria that result from detailed geological, geochemical and geophysical studies of both footwall and hanging wall rocks, studies that are not possible in modern sea floor environments. Nevertheless, seafoor research has contributed to our understanding of the growth of sulphide mounds, the mechanism of sulphide deposition and of the chemistry of fluids involved in VMS systems. In particular, the role of structure and of tectonic setting has been clarified through observation of active seafloor hydrothermal systems. In turn, observations made in land-based VMS research has helped seafloor researchers to focus on key issues which, will eventually contribute to improved exploration models.

Jan 1, 1998

By Robert G. Ditchburn

The NW caldera hydrothermal vent field at Brothers volcano, of the Kermadec-Tonga arc, has associated massive sulfide mineralization. This includes an abundance of black smoker chimneys that contain significant concentrations of copper, lead, zinc and gold (de Ronde et al., 2005; de Ronde et al, 2010, under review). [ ] The oldest volcanic massive sulphide (VMS) samples recovered so far from Brothers have been dated using radiometric methods at GNS Science and found to be c. 1000 years old. By contrast, a volcanic cone that has formed in the southern part of the caldera has no associated VMS. Only elemental sulphur and Fe-oxide crusts are present here, samples of which have been analysed for their trace elements. From d34S values of sulfates and native sulfur, and the volume of gas (dominated by CO2 and H2S) discharging at the cone site, elements being deposited here are considered more directly magmatic in origin (de Ronde et al., 2005; 2010 under review). It has been discovered that deep-seated changes in volcanic activity at Brothers affect the NW caldera and cone site simultaneously, though the mineralogy at each site is so very different. Thus, the cone site is being studied to determine if elements being deposited there can be used as predictors of potential future VMS mineralisation as similar sites have been found at other volcanoes along the Kermadec arc and elsewhere. The frequency of these deep-seated magmatic events is considered important in the formation of Cu-Au-rich mineralization along arcs. The analysis of Fe within resulting hydrothermal plumes (surveyed by surface vessels), and trace elements in rock and mineral samples, are used to help determine the influence of magmatic contributions to the hydrothermal system. To verify that plumes are a reliable proxy for hydrothermal events depositing iron on the seafloor, Fe-oxide crusts from Brothers volcano cone have been dated to see if their emplacement coincides with highly Fe-enriched plumes in the water column. The radiometric dating techniques developed for barite-rich VMS, i.e. using 228Ra and 226Ra, were unsuitable for the Fe-oxide crusts because 210Pb was the only isotope detected by gamma spectrometry. Therefore, new techniques using 210Pb, 10Be and arsenic have been established.

Jan 1, 2010

By K. T. Damodaran

The Chavara and Manavalakurichi placer deposits have been known since a long time for their rich reserves of heavy minerals like ilmenite, rutile, monazite etc. While detailed work has been conducted on the mineralogy and texture of the bulk placer sediments, reports on the detailed investigations on individual minerals are relatively scanty. Though, limited work pertaining to the chemistry of ilmenite has been carried out by Nair et al (1995) and Ramakrishnan et al (1997), a comprehensive study of the weathering patterns of ilmenite along the longitudinal and vertical profiles has not been, so far, undertaken. Data on the microscopic analysis of ilmenite from the southwest placers, too, is sketchy. The present work deals with the variation of the weathering undergone by ilmenite in the southwest placer deposits based on chemical and mineralogical analyses.

Jan 1, 2002

By Gale L. Hubred

Kennecott?s Ledgemont Laboratory developed the Cuprion Process to recover metal values from manganese nodules in the early 1970s. A reducing leach of monovalent cuprous ion attacks the manganese oxide matrix, converting the manganese dioxide to manganese carbonate and releasing the copper, nickel, cobalt, and zinc as ammine complexes. Cuprous ion is generated by contacting leach liquor with carbon monoxide. Copper, and nickel, are recovered by solvent extraction and electrowinning. Cobalt is precipitated as cobalt sulfide and recovered as cobalt powder. Manganese, molybdenum, and zinc can be recovered optionally but have not been included in this process. Kennecott authors have described aspects of the process, but the Cuprion process has not been revealed except in patents. Tables are included for capital and operating costs and revenue. Even though economic recovery of nodules is not anticipated in the foreseeable future, some of the process steps may have application in other places. The Ledgemont Laboratory was a unique operation we think worth documenting. The report is based upon work done up until the mid 1970s. The report represents the work of the entire Kennecott nodule team. It is this author?s intention to save this result and credit the work of that nodule team. The paper is dedicated to the memory of Dr. Herbert Barner, a key member of the team who died in 2003.

Jan 1, 2005

By Hal Palmer

A number of Articles contained in the United Nations Convention on the Law of the Sea III (UNCLOS) bear directly on legal issues related to the recovery of mineral deposits on the ocean floor. Mineral resources of the continental margin other than oil, gas and hydrates include, sand, gravel, shell, coral, gemstones and phosphorite. Jurisdiction over the exploration and exploitation of these deposits is determined either by the Territorial Sea claims of a coastal state or their recognized sovereign rights in the Exclusive Economic Zone (EEZ). At least 33 coastal states have the right under Article 76 (Continental Shelf regime) to claim seabed jurisdiction beyond 200 nautical miles (EEZ limit). In addition, several states have "Pioneer Investor" status with regard to seabed resources in international waters (The Area). A global maritime boundary database (GMBD) has been developed as a basic resource identifying the current claims of coastal states. It provides detailed information on existing boundaries and limits determined by the UNCLOS accords or by multi-lateral agreements which affect mineral exploration and exploitation. This paper will describe the GMBD and its construction and maintenance.

Jan 1, 2000

By Valcana Stoyanova

Deep-sea mining of polymetallic nodules are expected to produce serious impact on benthic ecosystem due to removal of nodules, sediments and associated fauna by means of collector, and subsequently, by the resettlement of sediment plume which may affect seabed biota outside mining tracks through blanketing, smothering and feeding interruption. The scale and magnitude of the exact impact of commercial operations is not known at present, but its assessment strongly required acquisition of the adequate environmental baseline information. During the past two decades, IOM carried out a total of 20 research cruises in the eastern part of Clarion-Clipperton Zone (CCZ) with purpose to obtain essential data and information on polymetallic nodules and to prepare for future development their deposits. Whilst evaluating the nodule coverage at particular station from both seafloor photographs and box-core recoveries it was ascertain that the ground-truth data plotted against the photo data indicated substantial differences between two methods. Understanding of this phenomenon has not only the methodology meaning related to the efficiency of the using photoprofiling techniques during exploration of nodules, but also it could be of environmental importance because the similarity between natural sediment blanketing occurrence in studied area and expected re-deposition and blanketing of sediments which will be disturbed during mining operations.

Jan 1, 2011

By Gordon B. J. Fader

A regional assessment of the aggregate potential of the Scotian Shelf is presently being funded through a Canada-Nova Scotia Cooperation Agreement on Mineral Development. This assessment includes testing of seabed materials for their suitability in a variety of concrete, asphalt and other specialized applications. The glacial and postglacial Holocene history of the Scotian Shelf has been favourable for the formation of large deposits of sand and gravel that have potential for use as marine aggregate resources. Large banks and inner shelf areas of the seabed consist of basal transgressive sand and gravel of the Sable Island Sand and Gravel Formation. These sediments accumulated during the late Wisconsinan postglacial transgression, through sorting of glacial materials that were originally deposited beneath marine terminating glaciers. Some sandy deposits occur as low-stand deltas on the inner shelf at 70 m water depth and were formed during the maxi- mum low sea level stand, in early postglacial time, at approximately 12 000 yBP. Modern sediment transport processes have contributed to the formation of areas of large sand bedforms, such as the Cape Split sand wave field and other isolated sand waves of the inner Bay of Fundy, and Eastern Shoal on Banquereau. Sandy sediments, found in many transverse channels in the nearshore, offer a potential for placer gold where proximal to adjacent onshore epithermal gold deposits. Lithothamnion covered gravel occurs as a thin lag overlying glacial sediments in much of the nearshore. Relict gravel beach ridges have been eroded and redistributed through sub-littoral processes after passage of the transgressing beach front. Multibeam bathymetry, sidescan sonograms and high-resolution seismic reflection profiles are the main survey tools. Ground truth consists of large volume seabed samples, vibrocores and photographs. A preliminary assessment of the aggregate potential indicates that very large volumes of suitable aggregate lie in the offshore of southeast Canada.

Jan 1, 1995

By Peter A. Rona

Investigations of the Gorda Ridge within the proclaimed U.S. Exclusive Economic Zone off northern California and southern Oregon, and the Mid-Atlantic Ridge extending along the center of the Atlantic Ocean, have received new impetus from the discovery of hot black smokers, sizeable polymetallic massive sulfide deposits, and vent animals at the Mid-Atlantic Ridge by the NOAA VENTS Program in 1985. Prior to that time, the oceanographic community focused investigations of seafloor venting at the faster-spreading oceanic ridges of the Pacific Ocean including the East Pacific Rise, the Galapagos spreading center and the Juan de Fuca Ridge because a consensus held that the faster spreading rates at these ridges were necessary to supply the heat to drive black smoker-type venting. As the only oceanic ridge in the Pacific with slow-spreading characteristics, the Gorda Ridge is an outlier of the slow-spreading ridge system that extends through the Atlantic Ocean and western Indian Ocean comprising more than half the 55,000-kilometer-length of the globe-encircling oceanic ridge system. In response to recent discoveries at the Mid-Atlantic Ridge the oceanographic community is shifting more of its activity to investigation of hydrothermal venting and related processes at slow-spreading oceanic ridges. The discovery cruise by a team of NOAA and university scientists followed by

Jan 1, 1988

By Frank Manheim

The purpose of this presentation is to review the history of offshore non- fisheries resource development since World War II, as an introduction to a planned symposium on offshore resources scheduled for the 1996 UMI Conference. After World War II the United States became the leader in offshore oil and gas production, deep ocean drilling technologies, offshore terminals, platforms and production systems, and natural gas recovery and transport. Wartime skills in acoustic profiling and antisubmarine warfare were transferred into commercially important geophysical exploration techniques. The application of ocean drilling and geophysical techniques permitted the recognition and elucidation of plate tectonics patterns, development of seafloor spreading theory, and the transformation of our knowledge of seabed and subseabed strata. After John Mero&apos;s studies and recommendations for developing marine manganese nodules in the late 1950&apos;s interest in nonfuel minerals grew rapidly. The formation of international deep sea mining consortia in the 1960&apos;s was accompanied by a flurry of ocean engineering development, minerals prospecting and associated environmental studies The Santa Barbara Oil Spill of 1969 resulted in a moratorium on both offshore energy and minerals leasing by the Depart- ment Interior, and catalyzed the development of new Federal legislation in 1972. In 1973 the offshore energy moratorium was lifted in response to the Arab oil embargo, and offshore energy activities surged for a time. Minerals were reopened to leasing following President Reagan&apos;s 1983 executive order implementing a 200 mile EEZ. Although interest was spurred by

Jan 1, 1995

By G. B. Carpenter

The United Nations Law of the Sea (LOS) Convention includes provisions (Article 76) for establishing the outer limits of a coastal State&apos;s continental shelf and for denoting the seaward extent of sovereign rights over natural resources. Determination of a coastal State&apos;s continental margin, according to Article 76, must consider eight factors: 1. The territorial sea baseline 2. The 2,500-meter isobath 3. The foot of the continental slope 4. A line 200 nautical miles seaward of the territorial sea baseline 5. A line seaward of the foot of the continental slope connecting the points where sediment thickness divided by distance to the foot of the slope equals .01 6. A line 60 nautical miles seaward of the foot of the continental slope 7. A line 100 nautical miles seaward of the 2,500-meter isobath 8. A line 350 nautical miles seaward of the territorial sea baseline Figure 1 shows the preliminary limits for each of the Article 76-based definitions for a portion of the U.S. Atlantic continental shelf. The additional areas gained beyond the 200- nautical mile Exclusive Economic Zone (EEZ) are highlighted. The first three factors are baselines from which the distance provisions of Article 76 are measured. Factors 4-8 are distance- from-baseline provisions for establishing the continental shelf limits. Factor 5, also known as the Depth of Sediment Limit or "Irish Formula", was calculated using sediment thickness data from seismic linesand isopach maps. All other factors were determined from digital hydrographic data. The Depth of Sediment Limit is the most advantageous method for the area shown in Figure 1. It is especially useful for introverted coastlines such as the Georgia Embayment and New York Bight areas. The 200-mile line is advantageous for protruding coasts such as those off major capes, e.g., Cape Hatteras. The 2,500-meter isobath plus 100-mile line gains

Jan 1, 1995